docs: def init_app(self, app):
          """
          To initiate with Flask
          :param app: Flask object
          :return:
          """
          provider = app.config.get("STORAGE_PROVIDER", None)
          key = app.config.get("STORAGE_KEY", None)
          secret = app.config.get("STORAGE_SECRET", None)
          container = app.config.get("STORAGE_CONTAINER", None)
          allowed_extensions = app.config.get("STORAGE_ALLOWED_EXTENSIONS", None)
          serve_files = app.config.get("STORAGE_SERVER", True)
          serve_files_url = app.config.get("STORAGE_SERVER_URL", "files")
  
          self.config["serve_files"] = serve_files
          self.config["serve_files_url"] = serve_files_url
  
          if not provider:
              raise ValueError("'STORAGE_PROVIDER' is missing")
  
          if provider.upper() == "LOCAL":
              if not os.path.isdir(container):
                  raise IOError("Local Container (directory) '%s' is not a "
                                "directory or doesn't exist for LOCAL provider" % container)
  
          self.__init__(provider=provider,
                        key=key,
                        secret=secret,
                        container=container,
                        allowed_extensions=allowed_extensions)
  
          self._register_file_server(app)